1. Field of the Invention
This invention relates to a microscope objective which is applicable to a microscope having high extensiveness that is capable of providing a high NA while having a wide observation range to acquire a feeble light signal at a high S/N ratio in microscopy, and to a microscope system provided with this microscope.
2. Description of Related Art
In the most advanced research field at present, various methods of observing cells, in vivo, for a long period of time (several days to several weeks) are developed for purposes of the functional clarification of living cells and the behavior analysis and interaction clarification of a protein. As one technique of microscopy for observing a lesion part inside a living cell, the method of making a fluorescence observation is largely used. The fluorescence observation is such that, after a particular fluorescent substance like a fluorescent protein is used as a light-emitting label to stain a living specimen like the living cell, fluorescent light is produced by irradiating the specimen with exciting light and is observed to thereby detect the existence and position of a particular part in the living specimen, such as the lesion part inside the living cell.
In general, an objective for biological microscopes is constructed so that an observation object (the specimen) is viewed through a cover glass and is designed so that, for example, aberration produced by the cover glass is corrected on the premise that the thickness of the cover glass has a constant reference value.
However, the cover glass is attended with a fabrication error. Depending on the observation technique, the observation object is sometimes viewed through a nearly plane-parallel plate of thickness different from that of the reference value, such as the cover glass or a Petri dish.
Thus, when the thickness of the cover glass is different from that of the reference value and is varied, aberration produced in accordance with variation of the thickness of the cover glass cannot be completely corrected by the objective and imaging performance is degraded. In particular, as the NA becomes high, the degradation of the imaging performance becomes pronounced.
However, conventional microscope objectives for correcting aberration produced in accordance with the variation of the thickness of the cover glass interposed between the surface of the observation object and the objective are set forth, for example, in Japanese Patent Publication No. Hei 03-58492 and Japanese Patent No. 3371934.
In the fluorescence observation, when some stimulus is given to the living specimen, for example, by the irradiation of exciting light, there is the possibility that the stimulus itself adversely affects an active state of the cell. Consequently, it is desired to provide a microscope system such that the light-emitting label is stimulated with the weakest possible stimulus (low-intensity exciting light) and a weak luminous signal produced in accordance with this stimulus can be detected at extremely high efficiency.
Simultaneously, it is also desired to provide a microscope system in which provisions are made for keeping a state of behavior of the living cell in sight and at the same time, detecting much information from the cell at a time through the observation in a wide range so that a processing speed and work efficiency can be improved.
In the field of conventional microscope apparatuses, however, microscope apparatuses fulfilling the above requirements and microscope systems provided with these microscope apparatuses have no existence. As such, the objectives set forth in the prior art references mentioned above are not constructed on the premise that they are applied to microscope apparatuses fulfilling the above requirements and microscope systems provided with these microscope apparatuses.
However, the applicant of the present invention, in Japanese Patent Publication No. 2007-41510 filed by this applicant, proposes the microscope fulfilling the above requirements, that is, the microscope having high extensiveness that is capable of providing a high NA while having a wide observation range to acquire a feeble light signal at a high S/N ratio and the microscope system provided with this microscope.
Even in such a microscope objective, it is desired to correct aberration produced in accordance with the variation of the thickness of the cover glass. In biochemical microscopy, the fluctuation of aberration may be caused not only by the variation of the thickness of the cover glass, but also by a difference with room temperature in the case where the microscope is used at the temperature of cell culture, and correction for the fluctuation of aberration is desired.